1. Field of Invention
The present invention relates to a kneading degree adjusting device for a twin extruder.
2. Related Art
FIGS. 6A-6C show one example of kneading degree adjusting devices in a conventional twin extruder. This kneading degree adjusting device in the twin extruder comprises a cylinder 101 and two screws 102 which are rotatably provided in the cylinder 101. A pair of gate valves 103a, 103b provided at a downstream side of a kneading part B so as to be movable perpendicularly to an axial direction (upward and downward in the drawings) are brought closer to or separated from each other by means of hydraulic cylinders 106a, 106b, whereby gaps formed between faces 102a at the root of a flight of the screws 102 and semicircular faces 104a, 104b formed at the tip ends of the gate valves 103a, 103b are changed in size, thereby to vary the kneading degree (Examined Japanese Utility Model Publication Hei. 7-56185).
In the above described conventional art, due to the structure that a pair of the gate valves are moved perpendicularly to the axial direction in order to change the gaps (hereinafter referred to as "opening degree variable channels") formed between the faces of the screws at the root of the flight and the semicircular faces formed at the tip ends of the gate valves, there have been such problems as described below.
A sectional shape of the opening degree variable channel varies from a substantially annular shape to a substantially oval shape, and the gaps between the semicircular faces of a pair of the gate valves and the faces of the screws at the root of the flight are subjected to a greater change in a vertical direction than in a lateral direction. As the result, an unmolten material having high viscosity is allowed to short-pass the larger gaps in an upper and lower parts, and thus a filling degree of the material in the kneading part upstream of the gate valves will become unstable. Therefore, a uniform kneading efficiency cannot be obtained.
Further, because the opening degree of the opening degree variable channel is changed by moving a pair of the gate valves perpendicularly to the axial direction of the cylinder, not only opening and closing times of the channels will be longer but also the structure will become complicated.